Also, I just checked a few iNat observations on GBIF, and all have WGS84 as the geodetic datum (even one of my observations where I pulled lat/lon off a paper topo map), so iNaturalist apparently assumes that this is the datum of locations entered by users.
So yes, data exported by iNaturalist does presume that the geodetic datum is WGS84 (EPSG 4326).